1. Field of the Invention
The present invention relates to an electronic device incorporating an electronic display, a keypad and ox more sources of light for illuminating the display and the keypad. In particular, the electronic device to which this invention relates is a mobile telecommunications device such as a telephone but it could also include any other type of electronic device that incorporates a keypad and an electronic display including, for example; a personal data assistant (PDA) or other electronic device such as a television/stereo remote control unit. For ease of understanding, the invention will be described hereinafter in its application to a mobile telephone.
2. Description of the Prior
A conventional mobile telephone includes an electronic display such as an LCD and a keypad. The keypad includes a plurality of keys formed on a flexible mat which are accessible through apertures in the front cover of the mobile telephone, and a key pad membrane attached to a substrate beneath the keys. The key pad membrane has a pin or other protuberance located beneath each key which deforms a conductive element into contact with a printed circuit board situated beneath the substrate when the key is depressed. An electrical circuit is thereby closed and the selected function is performed. One ox more light sources such as LFD's are located adjacent to the display around its periphery and in the vicinity of the keypad so that the display and the key pad are illuminated when the telephone is in use. At least a portion of each key is formed from a translucent or light transmitting material so that they are visibly illuminated from the front.
A problem with this known arrangement is that a relatively large number of LED's or other light sources are required between the keys and surrounding the display to ensure that a uniform or homogeneous lighting effect is created: over the whole keyboard as well as the display. Furthermore, “hot-spots” or regions of the display and keypad which are illuminated to a greater intensity than other regions ale often produced in the immediate vicinity of the light sources. Not only do the LED's and their associated circuitry take up more space within the telephone but its manufacture is more complicated, it is heavier and battery life is reduced due to an increase in power consumption.
Attempts have been made to overcome the aforementioned problem by reducing the number of light sources positioned beneath the keys and instead relying on the light sources surrounding the periphery of the display to illuminate both the display and the keypad. This has been achieved by incorporating lenses, other optical devices or light scattering surfaces in the telephone casing around the keypad so that part of the light matted by the light sources is out-coupled to the keypad thereby illuminating both the display and the keypad. However, it has been found that this solution is unsatisfactory as the intensity of the light noticeably reduces with distance away from the light source resulting in a non-uniform lighting effect across the keypad.
Another problem with conventional mobile telephones is that due to the close proximity of the keys and the printed circuit board, high stresses are created in the printed circuit board when excess pressure is applied to the keys which may occur when, for example, a user is playing a game or writing a text message. This can eventually cause damage to the printed circuit board and malfunction of the telephone.
U.S. Pat. No. 4,755,035 discloses a display assembly for an LCD in which the LCD element is mounted on the top surface of a carrier made from light transmitting material. A point light source is positioned adjacent to the carrier so that light emitted from the source is transmitted through the carrier to backlight the display. The carrier is wedge shaped to ensure uniform backlighting across the LCD.
U.S. Pat. No. 5,075,824 discloses as LCD/light wedge module in which an LCD is received in a pocket of a wedge shaped carrier. The carrier has a pair of openings to receive point light sources so that light emitted from the sources is directed onto the slanted rear surface of the wedge and is reflected towards the LCD so as to provide a more uniform backlighting effect across the LCD.
U.S. Pat. Nos. 4,755,035 and 5,075,824 both disclose arrangements for providing a more uniform backlighting effect across an electronic display. However, neither document discloses an arrangement in which the light source is configured to illuminate both the display and a keypad with a more uniform light.